The license tax on a company commencing business in the Commonwealth shall be measured by an estimate of direct gross premium income reasonably expected to be derived from such business in the Commonwealth from the time of commencing business to December 31 following. Every estimate made under this section shall be subject to review by the Department after the close of the year for which the estimate is made and, if there is any variance between the estimate and the actual direct gross premium income, the Department shall issue a refund or provide notice of the assessment of additional license tax depending on whether such estimate was in excess of or less than the actual direct gross premium income of such company for such year.